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<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        // 全局变量 不推荐定义过多；
        // 全局污染；
        {
            var a = 10;
            var b = 20;
            function test() {
                var bar;
                bar = "str";  //及其不推荐
            }

        }



    </script>
</body>

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